What is it about?
We investigated how DNA replication finishes when two E. coli replication forks meet at a Tus-ter barrier, part of the bacterial replication fork trap. Using a reconstituted plasmid-based replication system in vitro, we controlled one fork stalled at Tus-ter and then released the other fork to meet it. A mapping assay showed that this type of fork fusion did not copy every base: a short 15–24 base stretch of template DNA remained unreplicated. Adding lagging-strand processing enzymes, or the helicases Rep, UvrD and RecG, did not complete the reaction in this system.
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Why is it important?
Accurate completion of DNA replication is essential for genome stability, but the final step where replication forks meet is still not fully understood. Our results suggest that when termination is forced to occur at Tus-ter, the established replication machinery is not sufficient on its own to finish copying the DNA. This points to the need for additional processing steps in E. coli and helps explain why the replication fork trap may create both useful control and extra constraints during chromosome duplication.
Perspectives
From our perspective, what stands out is that we could build an in vitro system where fork fusion at Tus-ter could be controlled and mapped directly. This allowed us to separate simple fork blocking from the specific problem created when two forks meet at a Tus-ter complex. It was also striking that the obvious candidate enzymes and helicases did not close the gap, leaving a clear question about how this final stretch of DNA is completed in cells.
Dr. Christian J Rudolph
Brunel University
Read the Original
This page is a summary of: Termination of DNA replication at Tus-ter barriers results in under-replication of template DNA, Journal of Biological Chemistry, December 2021, Elsevier,
DOI: 10.1016/j.jbc.2021.101409.
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